BEIRUT (AFP) - At least 35 ISIS (Islamic State in Iraq and Syria) extremist militants were killed on Sunday in clashes with Syrian Kurdish fighters around the flashpoint town of Kobane, a monitor said.

The Syrian Observatory for Human Rights said the deaths came in three separate clashes around the town in Aleppo province of northern Syria.

At least 22 of the extremists were killed in fighting on the border between Aleppo and Raqa province, where IS has its de-facto capital.

That battle marked the first time in months that fighters from the Kurdish People's Protection Units (YPG) have expanded their attacks to the edge of Raqa province.

Four YPG fighters were killed in those clashes, with the Kurdish forces capturing the strategic Tal Baghdaq hilltop, the Observatory said.

The other extremist deaths came in clashes to the west and south of Kobane, the key border town that Kurdish forces recaptured on January 26.

ISIS fighters began advancing on the town last September, and at one point looked poised to overrun it, cementing their grip on a long stretch of the Syria-Turkey border.

But YPG ground forces backed by US-led air strikes were able to repel the ISIS fighters.

Since the town's recapture, YPG forces have been expanding their control from Kobane into the surrounding countryside, where they have largely encountered little resistance from the militant extremists.

But the Observatory said the fighting around Tel Baghdaq on the Aleppo-Raqa border was some of the heaviest in the region since Kobane fell.

The group said the US-led coalition fighting ISIS had also carried out air strikes in the region on Sunday, but there was no initial information on casualties in the raids.

The ISIS group has declared an Islamic "caliphate" in territory it controls in Syria and Iraq, with the provincial capital of Raqa province serving as its effective capital.

More than 210,000 people have been killed in Syria since the country's conflict began with anti-government demonstrations in March 2011.